<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
  var A = function () {
    this.a = 2;
  }
  console.log(A.prototype);
  var a = new A();
  console.log(a);
  console.log(a.s);
</script>
</body>
</html>
